Dynamic loudspeaker systems typically use a main panel to carry a speaker driver or acoustic transducer and an enclosure behind the driver. The main panel may be on the front, a side, or the bottom. The driver has a diaphragm driven by a voice coil and magnet, sometimes called a motor, to move the ambient air outside the enclosure, creating sound waves. Air is moved both in front of and behind the diaphragm. The air in front of the diaphragm generates sound waves into a room or another listening environment. The air behind the diaphragm is in the enclosure.
Different enclosure designs handle the sound waves that come off the back of the diaphragm. While some systems do not use an enclosure, an enclosure can extend the bass response or improve the efficiency of the loudspeaker system. A sealed acoustic suspension enclosure uses the air in the enclosure to generate spring resistance against the diaphragm of the acoustic transducer. A bass reflex or tuned port enclosure allows the sound waves in the enclosure to escape through a carefully designed port with a delay. A passive radiator is used in a sealed enclosure as an alternative to a port. It is similar to an electrodynamic acoustic transducer but has no active voice coil. The sound waves in the enclosure drive the back side of the passive radiator diaphragm. The front side of the passive radiator creates sound waves into the listening environment.
The various known enclosure designs provide different advantages and disadvantages. The perceived quality of a particular design is difficult to predict. Music reproduction is complex and cannot be fully and accurately modeled. The sounds from different voices and musical instruments reinforce and interfere with one another in a complex way that changes as the sounds change through a musical passage. Each person's perception of the quality and accuracy of the same reproduced sounds can also differ. There are also variations in how sound is recorded, stored, derived from storage, and amplified into the voice coil. Different dynamic drivers also differ. As a result, different designs are preferred for reproducing different sounds by different people and many different types of enclosure designs continue to sell. Reproduction inaccuracies added by an enclosure or by diaphragm mounting may be perceived as adding warmth or impact or as compensating for another weakness in the complete system from source material to sound.